The present invention relates to a technical field of an electrostatic ink jet recording system, in particular, an ink jet recording apparatus and an ink jet recording method with which recording is performed onto a recording medium by ejecting ink by means of electrostatic force.
An electrostatic ink jet recording system is a system in which an image is formed on a recording medium by ejecting ink droplets through exertion of electrostatic force on ink in accordance with an image signal and has the following features: simplicity of a head structure; easiness of realization of a multi-channel construction; ability to form fine droplets; and ability to perform high-resolution drawing. As to such an electrostatic ink jet recording system, for instance, U.S. Pat. No. 6,817,692 B (hereinafter referred to as “Patent Document 1”) relates to an ink jet recording method, with which the density of ink in the vicinity of openings is increased through electrophoresis of charged particles in an ink flow path and ejection is performed, and discloses an ink jet recording apparatus that includes an ink jet head that performs ejection of ink droplets by means of electrostatic attractive forces mainly ascribable to a recording medium or a counter electrode arranged on the back of the recording medium.
FIG. 18 is an outlined diagram showing a construction of the multi-channel ink jet head disclosed in Patent Document 1 and shows a cross section of an ejection electrode corresponding to a recording head. In the drawing, oil-based ink Q is supplied to a space between a head substrate 202 and an ejection electrode substrate 203 from an ink circulation mechanism 211 including a pump through an ink supply flow path 212 connected to a head block 201, and is recovered to the ink circulation mechanism 211 through an ink recovery flow path 213 also connected to the head block 201. The ejection electrode substrate 203 includes an insulative substrate 204 in which a through hole 207 is formed, and an ejection electrode 209 formed on a surface of the substrate 204 on a recording medium P side to surround the through hole 207.
On the other hand, on the head substrate 202, a projection-shaped ink guide 208 is arranged at substantially the center position of the through hole 207. The projection-shaped ink guide 208 is obtained using an insulative member made of a plastic resin, ceramic, or the like, arranged at the same row interval and pitch so that the center of the ink guide 208 coincides with the center of the through hole 207, and is held on the head substrate 202 with a predetermined method. Each projection-shaped ink guide 208 has a shape in which the tip end of a flat plate having a constant thickness is cut into a triangular shape or a trapezoidal shape, and its tip end portion serves as an ink droplet flying position 210. An ink meniscus is formed between the ink guide 208 and the inner wall surface of the through hole 207. A recording medium P is arranged on a conveyor belt 222 so that it opposes the tip end of the projection-shaped ink guide 208. Also, in a bottom portion of the space between the head substrate 202 and the ejection electrode substrate 203, a migration electrode 205 is formed.
In the ink jet head, at the time of recording, the ink Q supplied from the ink circulation mechanism 211 through the ink supply flow path 212 is supplied to the ink droplet flying position 210 at the tip end of the projection-shaped ink guide 208 through the through hole 207 and a part of the ink Q is recovered to the ink circulation mechanism 211 through the ink recovery flow path 213. Here, to the ejection electrode 209, as a signal voltage corresponding to an image signal from a signal voltage supply 223, a pulse voltage of +500 V is applied at ON time, for instance. When doing so, a voltage of +300 V is applied to the migration electrode 205. On the other hand, the recording medium P is charged to a voltage of −1.7 kV by corona charging means. Now, when the ejection electrode 209 is placed under an ON state (state under which 500 V is applied), an ink droplet R is ejected from the ink droplet flying position 210 at the tip end of the projection-shaped ink guide 208, flies toward the recording medium P, and forms a dot of an image.
With the ink jet recording apparatus disclosed in Patent Document 1, it becomes possible to suppress blurring due to absorption of ink into paper, reduce limitations as to the recording media used, and record images on various recording media.
In addition, coloring particles with increased density are ejected, with the result that a high-density and clear image free from blurring is formed, so it becomes possible to form a high-resolution image not only on dedicated paper for ink jet printing but also on ordinary offset printing paper, plastic film, printing plate for printing, and the like.
The electrostatic ink jet recording apparatus disclosed in Patent Document 1 has the superior features described above, however, it also has a problem that the state of the ink meniscus formed at the ejection port at the time of ejection changes due to an ejection history and the diameter of a formed dot changes, that is, because ink droplet ejection characteristics have ejection frequency dependence (dependence on the number of times of ejection), there are cases where the ejection characteristics change due to the frequency of ejection at each ejection portion.
When the ejection characteristics become unstable in this manner, there occurs a problem that images are not formed on recording media in a constant manner and it becomes impossible to form high-quality images.
The above problems can be solved with a method with which an ejection signal is controlled with reference to an ejection history, however, the method has a problem that a driver becomes complicated and an increase in cost is inevitable.